Honeywell FMS
Thread Starter
Join Date: Nov 2004
Location: Canada
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Honeywell FMS
On the Honeywell FMS, is there a page that one can look at to figure out what kind of descent rate the aircraft will use if in VNAV mode? For example, if you are asked to cross XYZ at 10,000 feet, and you want to use vertical speed as opposed to VNAV, where could you find the required descent rate?
FMS
FMS
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
On the 737 (Smith's, I think?) the descent page gives a figure (which doesn't work very well
) bottom right of the screen (courtesy of Cpt SandL's site.) just above 'SPEED>'. It is a good starting point, and then the 'Green arc' as 'I' says.
Presumably there is something similar on the Honeywell.
http://www.b737.org.uk/images/fmc_path_des.gif
) bottom right of the screen (courtesy of Cpt SandL's site.) just above 'SPEED>'. It is a good starting point, and then the 'Green arc' as 'I' says.Presumably there is something similar on the Honeywell.
http://www.b737.org.uk/images/fmc_path_des.gif
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,499
Likes: 0
Received 0 Likes
on
0 Posts
Allways be aware however that that VS is only computed to the waypoint/altitude restriction above it and only on a direct course towards that waypoint. So yes, it can be quite a bit off, but it can work quite well too. It often is not what VNAV computes and does.
Join Date: May 2000
Location: Seattle
Posts: 3,196
Likes: 0
Received 0 Likes
on
0 Posts
If the 777 FMS is anything like the 744's, that 1250 FPM is only for the "Descend Now" mode, where an early descent is manually forced prior to (but within 50 NM of) the calculated TOD. Once the VNAV Path is reached, the descent rate is more like 3000 FPM at altitude and 2000 FPM down low (just prior to the decel at 10,000').
Buttonpusher
I think it's on the DES page at the bottom (if the software is there) there is FPA (Flight path angle) and the VS which shows the required rate to make the restriction.
At least thats what's on the Honeywells we use.
Standing by to be corrected....
At least thats what's on the Honeywells we use.
Standing by to be corrected....
Join Date: Apr 2008
Location: Sand on the Rocks !
Age: 41
Posts: 111
Likes: 0
Received 0 Likes
on
0 Posts
Same in our 737-800s
Once DES page is active, below the FPA/VB line [5R i think], we get the required RoD to meet the active Waypoint Altitude Restrictions.
Once DES page is active, below the FPA/VB line [5R i think], we get the required RoD to meet the active Waypoint Altitude Restrictions.
Guest
Posts: n/a
FMS Guide,
The VS shown on the DES page of the FMS gives you the average vertical speed required to reach the next waypoint on your LEGs page with an altitude restriction, and this only at present groundspeed.
Let's assume you have a flightplan in the FMS with the only altitude restriction at your GS intercept waypoint, totally unrealistic but for the understanding required.
Further, let's assume this GS--27 (as we want to call this waypoint now) shows a restriction with 2000 ft.
You commence your flight and as soon as you climb through 2000 ft the FMS starts calculating your required vertical speed to reach this GS--27 waypoint at the 2000 ft restricted height. This is purely based on known aircraft data plus groundspeed data. There are no inputs of extra mileage requirements of a possible speed 250 at 10000ft restriction etc.
In VNAV mode the calculation basically works likewise, however, the FMS calculates a completely engine idle approach, in ideal conditions this will be a CDA approach with the thrust levers advancing just before reaching the GS--27 waypoint (assuming you followed the flap schedule as the FMS will give you).
However, the FMS needs a few more data to be more accurate. On the DES forecast page you need to complete the empty fields with winds at various altitudes, the OAT deviation and the QNH. The FMS will provide an idle power descend from your cruising level, it will automatically reduce speed at the pre-programmed altitude (250 / 10000ft) and of course for the flap schedule it calculates.
The calculation is based of the programmed routing, the ambient conditions at your present level as well as at the landing field as per forecast page.
In VNAV you will have a high vertical speed at intitial descend, expect not more than 1700 ft below 10000 ft in clean config.
This happens, of course, when following the descend profile in SPEED mode. Using PATH mode the FMS will follow the path indicated and should adjust thrust required to maintain this path. In older software versions this may happen a tad too late and a speed disconnect may occour, reverting the system into MCP mode which means idle power, high V/S rate...followed by a pilot's "What the f. " announcement.....
The VS shown on the DES page of the FMS gives you the average vertical speed required to reach the next waypoint on your LEGs page with an altitude restriction, and this only at present groundspeed.
Let's assume you have a flightplan in the FMS with the only altitude restriction at your GS intercept waypoint, totally unrealistic but for the understanding required.
Further, let's assume this GS--27 (as we want to call this waypoint now) shows a restriction with 2000 ft.
You commence your flight and as soon as you climb through 2000 ft the FMS starts calculating your required vertical speed to reach this GS--27 waypoint at the 2000 ft restricted height. This is purely based on known aircraft data plus groundspeed data. There are no inputs of extra mileage requirements of a possible speed 250 at 10000ft restriction etc.
In VNAV mode the calculation basically works likewise, however, the FMS calculates a completely engine idle approach, in ideal conditions this will be a CDA approach with the thrust levers advancing just before reaching the GS--27 waypoint (assuming you followed the flap schedule as the FMS will give you).
However, the FMS needs a few more data to be more accurate. On the DES forecast page you need to complete the empty fields with winds at various altitudes, the OAT deviation and the QNH. The FMS will provide an idle power descend from your cruising level, it will automatically reduce speed at the pre-programmed altitude (250 / 10000ft) and of course for the flap schedule it calculates.
The calculation is based of the programmed routing, the ambient conditions at your present level as well as at the landing field as per forecast page.
In VNAV you will have a high vertical speed at intitial descend, expect not more than 1700 ft below 10000 ft in clean config.
This happens, of course, when following the descend profile in SPEED mode. Using PATH mode the FMS will follow the path indicated and should adjust thrust required to maintain this path. In older software versions this may happen a tad too late and a speed disconnect may occour, reverting the system into MCP mode which means idle power, high V/S rate...followed by a pilot's "What the f.
" announcement.....
Join Date: Apr 2000
Location: BC
Posts: 450
Likes: 0
Received 0 Likes
on
0 Posts
On the 773-ER, one needs to go to VNAV, page 3. Once the aircraft is in a VNAV descent, you will see the FPA, VS and Path Deviation on the bottom line. The parameters are referenced to the active altitude restriction that is found on the legs page.
